The ionization potential of hydrogen atom is 13 . 6   V . How much energy need to be supplied to ionize…

Ionization energy is the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule.

Energy of an orbit is inversely proportional to the square of principal quantum number, $E\propto \frac{1}{n^2}$

$\Rightarrow \frac{E_2}{E_1}=\frac{{n_1}^2}{{n_2}^2}$

$\Rightarrow E_2=\frac{E_1}{2^2}$

$\Rightarrow E_2=\frac{13.6}{4}$

$\Rightarrow E_2=3.4 \mathrm{eV}$